In the prior art, for wireless communications by infrared and ultrasonic transmitters, the infrared and ultrasonic carrier signals are generated in different ways, for instance by oscillators. However, the frequency of the carrier generated this way needs to be adjusted and thus inconvenient for utilization. FIG. 1 shows the circuit diagram of a conventional carrier signal generator for infrared or ultrasonic transmission, in which the output of an integrated circuit 10 is connected to a complicated carrier generator 13 and an infrared light emitting diode (LED) or ultrasonic transducer 12, the carrier generator 13 for production of the carrier signal for infrared or ultrasonic output and the infrared LIGHT EMITTING DIODE or ultrasonic transducer 12 for transmission of the carrier signal. However, the frequency characteristics of the infrared LIGHT EMITTING DIODE and the ultrasonic transducer are different, once one transmission type has been determined, for example the ultrasonic one, the circuit must be modified to switch to the other transmission type. Therefore, the user has to choose the transmission type first and then design the circuit for producing the carrier, and thus it is more difficult to design the circuit.
Due to the shortcomings of the prior arts, it is desired an ultrasonic and infrared transmitter with tunable carrier frequency.